The present invention relates to a semiconductor integrated circuit for communication having therein a modulation circuit for modulating a carrier wave signal with a transmission baseband signal and, further, to a technique for cancelling a DC offset of a modulation circuit. More particularly, the invention relates to a technique effectively applied to a semiconductor integrated circuit for communication which is mounted on a radio communication system such as a cellular phone having a mode of modulating only a phase component and a mode of modulating a phase component and an amplitude mode.
In a radio communication system such as a cellular phone, a semiconductor integrated circuit for communication (hereinbelow, called an RF IC) is used, which down-converts/up-converts frequencies by mixing a local oscillation signal (carrier wave signal) of high frequencies with a reception signal or a transmission baseband signal by a mixer, modulates a transmission signal, and demodulates a reception signal.
A radio communication system of the GSM (Global System for Mobile Communication) or the like in recent years is being practically used, which has a mode called EDGE (Enhanced Data Rates for GMS Evolution) including not only a GMSK (Gaussian filtered Minimum Shift Keying) modulation mode of modulating a phase component of a carrier wave but also a 3π/8 rotating 8-PSK (Phase Shift Keying) modulation mode of modulating a phase component and an amplitude component of a carrier wave, and which can perform communications while switching the modulation modes. In the EDGE mode, not only phase modulation but also amplitude modulation is performed, so that data communication can be performed at higher speed than the GMSK mode performing only phase modulation.
In recent years, there is a demand for a dual-band cellular phone capable of using not only a signal according to the GSM but also a signal according to the WCDMA (Wideband Code Division Multiple Access) that uses spread spectrum as a multiplex method and uses the QPSK (Quadrature PSK) as a modulation method (Japanese Unexamined Patent Publication No. Hei 11 (1999)-205401).